💰 Finance calculator

Interest Expense Calculator

Calculate interest expense for any debt balance, annual rate, and time period. Choose days, months, quarters, or years — with 360 or 365 day basis for daily calculations. See total interest expense, the effective period rate, optional extra fees, and a multi-period cost comparison showing what the same loan costs weekly, monthly, quarterly, and annually.

Enter your debt details

Use a preset or enter your own values. Works for any type of debt — working capital loans, credit lines, equipment notes, bridge financing.

🔵 Debt details
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Outstanding balance used to calculate interest
%
Nominal annual rate stated in the loan agreement
🟢 Time period
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Number of periods to calculate interest for
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Unit for the period length above
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Used when period is in days
⚪ Optional
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Origination fee, service charges, etc.

Interest expense formula

Simple: Interest = P × r × t
Monthly: P × (r ÷ 12) × months
Daily: P × (r ÷ 360) × days
P = principal · r = annual rate · t = time

360 vs 365 day basis

Actual/360 — common in US commercial lending and money markets. Produces slightly higher effective cost because the same rate is divided by 360 instead of 365, so more interest accrues per day. Actual/365 — used in most personal loans and bonds.

Tip: interest expense in accounting refers to the cost of borrowed funds accrued during a period — regardless of when cash is paid. For the income statement, use the period-based calculation here. For cash paid, also account for timing of actual payment dates relative to the accrual period.
This is an educational estimate only. Real borrowing costs may differ based on compounding terms, average daily balances, payment timing, default charges, taxes, promotional rates, and lender-specific rules. Always review the full loan agreement for the actual cost of borrowing.

Frequently asked questions

What is interest expense?

Interest expense is the cost a borrower pays to a lender for the use of borrowed funds over a period. In accounting, it appears on the income statement as a non-operating expense and represents the accrued cost of debt — whether or not cash has been paid yet.

What is the formula for interest expense?

Simple interest expense = Principal × Annual rate × Time. For monthly calculations: Principal × (Annual rate ÷ 12). For daily calculations using a 365-day year: Principal × (Annual rate ÷ 365) × Days. Using a 360-day year: Principal × (Annual rate ÷ 360) × Days.

What is the difference between Actual/360 and Actual/365?

Both methods use the actual number of days in the calculation period, but divide by a different denominator for the annual basis. Actual/360 is common in US commercial lending and produces a slightly higher daily interest rate because the same annual rate is spread over fewer days. Actual/365 is used in most personal loans, mortgages, and bonds.

Is interest expense tax deductible?

In most jurisdictions, business interest expense is deductible from taxable income, reducing the net cost of borrowing. Personal mortgage interest may also be deductible depending on your tax situation and local rules. This calculator shows gross interest expense — consult a tax advisor for after-tax cost of borrowing.

Related finance calculators

Blended Interest Rate Calculator Combine multiple debt balances and rates into a single weighted average borrowing rate. Compound Interest Calculator Model how debt compounds over time when interest is added to the principal balance. Margin Calculator Calculate operating margin — interest expense reduces net margin from operating income. Tax Revenue Calculator Model tax impact — interest expense reduces taxable income and affects after-tax cost.

Disclaimer

This calculator is for educational and planning purposes only. It does not provide accounting, tax, legal, or financial advice. Actual interest expense may differ based on compounding frequency, average daily balances, payment timing, fees, and lender-specific terms. Always verify with your loan agreement and consult a qualified professional for formal accounting or tax decisions.